(1) Field of the Invention
The present invention relates to a thermoplastic resin composition which can provide molded articles having excellent mechanical properties, particularly improved impact resistance, and a method for preparing the same. This composition of the present case can be widely utilized as materials for industrial parts, electrical and electronic machine parts, automobile parts and the like.
(2) Description of the Prior Art
Aromatic polyester resins typified by polyethylene terephthalate resin and polybutylene terephthalate resin are excellent in mechanical properties, heat resistance, chemical resistance and the like but are poor in impact resistance, particularly notched impact strength. Therefore, improvement has been attempted. In the following examples of many attempts, the impact resistance is improved to some extent: a method for blending a copolymer which comprises monomers such as an .alpha.-olefin and an .alpha.,.beta.-unsaturated acid glycidyl ester disclosed in Japanese Patent Unexamined Publication No. 51-144452 (U.S. Pat. No. 4,172,859), WO 85/03718, WO 85/05117, U.S. Pat. No. 4,461,871 and Japanese Patent Unexamined Publication Nos. 52-32045 and 53-117049; a method for blending a modified polymer prepared by graft-reacting a monomer such as an .alpha.,.beta.-unsaturated acid glycidyl ester to a copolymer comprising an .alpha.-olefin and a non-conjugated diene disclosed in Japanese Patent Unexamined Publication No. 60-40154; and a method for blending a modified polymer prepared by graft-polymerizing an .alpha.,.beta.-unsaturated dicarboxylic acid, dicarboxylic anhydride, an imide derivative or the like to a copolymer of ethylene and an .alpha.-olefin having 3 or more carbon atoms disclosed in Japanese Patent Publication No. 57-54058.
However, the above modified .alpha.-olefin copolymer as an improver of impact resistance is a substantially rubbery polymer and has a glass transition temperature of room temperature or less. Therefore, in order to heighten the impact resistance, it is conceived to increase the amount of the modified .alpha.-olefin copolymer, but if the content of the latter is merely increased, heat resistance which is one of characteristics of the aromatic polyester resins, deteriorates.
In addition, molded articles of the aromatic polyester resin with which the above-mentioned .alpha.-olefin copolymer is blended have the excellent impact resistance immediately after molding, but when the molded articles are, for example, annealed to remove strain generated during the molding, the impact resistance becomes extremely degrade.
The inventors of the present application have intensively conducted research with the intention of eliminating the conventional drawback, and they have found that a thermoplastic resin composition prepared by blending an aromatic polyester resin with a specific thermoplastic resin having a multi-phase structure can improve impact resistance, maintaining heat resistance high, and can have improved impact strength even after annealing, and that the new thermoplastic resin composition can be effectively manufactured by melting and kneading the raw materials at a specific temperature. In consequence, the present invention has been completed on the basis of this knowledge.